The 3rd Generation Partnership Project (3rd Generation Partnership Project, 3GPP) launches an evolved packet system (Evolved Packet System, EPS) on the basis of the existing 2G and 3G networks. During early construction of an EPS network, an operator already has a mature circuit switched (Circuit Switch, CS) network and the EPS network only processes a data service. In view of protection of CS investment and a deployment strategy of the EPS network, the operator may use an original CS domain device to provide a CS service. Based on such a need, the 3GPP brings out a CS fallback (Fallback) technology, that is, when the CS service needs to be processed, a terminal covered by an evolved UMTS territorial radio access network (Evolved UMTS Territorial Radio Access Network, E-UTRAN) is handed over to the CS network to complete service processing. In this way, an objective that the existing CS domain device is reused to provide a conventional CS service for a user in the EPS network is achieved.
A short message service is an important constituent part of CS services at present. The operator hopes to continue to provide the existing short message service in the EPS network and implement mobile originating (Mobile Originating, MO) and mobile terminating (Mobile Terminating, MT) short message services. Moreover, because a terminal is frequently handed over between different access networks in areas where the E-UTRAN overlaps or is neighboring to a GSM/EDGE radio access network (GSM/EDGE Radio Access Network, GERAN) or a UMTS terrestrial radio access network (UMTS Terrestrial Radio Access Network, UTRAN), which results in large quantities of invalid location update signaling, and increases a signaling load of an air interface. The 3GPP introduces an idle state signaling reduction (Idle State Signaling Reduction, ISR) mechanism, which reduces the location update signaling, which is caused by frequent network handover, in a manner of double registration of the terminal with different access networks within a certain range.
When ISR is active, a mobility management entity (Mobility Management Entity, MME) initiates a paging (Paging) message, where the paging message carries a packet switched (Packet Switch, PS) domain indication, to the terminal through the E-UTRAN after receiving a paging message from a mobile-services switching centre (Mobile-services Switching Centre, MSC). Meanwhile, the MME sends a paging indication message to an associated serving general packet radio service (General Packet Radio Service, GPRS) support node (Serving GPRS Support Node, SGSN). The SGSN sends a paging message carrying a CS domain indication to the terminal through the GERAN or UTRAN. The terminal executes a corresponding service according to the domain indication in the paging message.
However, many problems exist in the prior art. For example, in a scenario of the mobile terminated short message service, if the terminal is performing a PS service when receiving the paging message of the SGSN, the terminal suspends the ongoing PS service after receiving the paging message that carries the CS domain indication, and returns to a CS domain to receive a short message, thereby resulting in an interruption of the current PS service of the user.